A magnetic disk controller which, when reading data corresponding to each sector from a magnetic disk apparatus, transfers ID information regarding the sector before transferring the data of the sector has been proposed as, for example, in Japanese Patent Application publication No. 7-141113.
When writing data from a host into a magnetic disk, a magnetic disk controller obtains the address of a sector to which the data is to be written, and calculates an error check code based on the obtained address and the data to be written into the sector. Hence, the magnetic disk controller can not write the data and error check code into the sector immediately after obtaining the address of the sector. Accordingly, the magnetic disk controller keeps on hold the writing of the data and error check code until the sector comes back to the position of the magnetic head, which delays the writing of the data and error check code.